Development of chemopreventive strategies for tobacco-related cancers has become a priority since smoking remains the major risk factor for lung cancer and the number of former smokers continues to increase in the US. The established A/J mouse model of cigarette smoke-mediated lung tumorigenesis, in which an increase in lung tumors occurs after the cessation of smoke exposure, provides a unique opportunity to develop preclinical chemopreventive regimens for former smokers. The hypothesis of the proposed studies is that tobacco carcinogenesis is the result of multiple synergistic, additive and antagonistic interactions among various tobacco smoke constituents. It then follows that exposure to multiple chemopreventive agents will be required to protect against smoke-induced DNA damage and tumor development. We propose to utilize the cigarette smoke-mediated lung tumorigenesis mouse model to identify intermediate endpoints or biomarkers of disease and test the efficacy of mixtures of chemopreventive agents in inhibiting molecular and cellular events associated with lung carcinogenesis. In Aim 1, numerous naturally occurring, and synthetic agents will be screened in vitro for their ability to inhibit oxidative DNA damage induced by cigarette smoke. Agents showing promise in these experiments will be tested in vivo for their effect on stress-related gene expression and DNA repair. Based on the resulting data, three mixtures of chemopreventive agents will be selected and tested in the A/J mouse model for their efficacy in inhibiting lung tumor indices (multiplicity and incidence) when administered following smoke cessation. The impact of smoke and/or the chemopreventive agent mixture on gene expression profiles, oxidative DNA damage burden, DNA repair and the frequency of gene mutations will also be evaluated. It is anticipated that these comprehensive analyses will provide the basis for the future development of a clinical regimen for the chemoprevention of lung tumors in former smokers.